Chitosan is a linear copolymer of D-glucosamine (2-amino-2-deoxy-D-glucose) and N-acetyl-D-glucosamine (2-acetamido-2-deoxy-D-glucose), obtained by partial (usually >80%) deacetylation of chitin, the main component of exoskeletons of insects and crustaceans. Chitosan has a low oral toxicity (oral LD50: >10,000 mg/kg in mouse and >1500 mg/kg in rats) and has been used as a component in various dietary supplements. In addition, chitosan is safe for topical use and has been used as an ingredient of medical devices or cosmetics. Chitosan is considered to be a safe and biocompatible material, and has been widely explored as a pharmaceutical excipient for a variety of applications such as wound healing, surgical adhesives, mucoadhesive oral drug/gene delivery, gene delivery, and tissue engineering.
Furthermore, chitosan is known to have a pKa of approximately 6.5. Therefore, chitosan is insoluble at a neutral pH but is positively charged and water-soluble at an acidic pH. Although the limited solubility of chitosan at a neutral pH is hypothesized to allow for formation of nanoparticle drug/gene delivery platforms, such limited solubility is disadvantageous for applications of a solution of chitosan at physiological conditions.
In addition, some studies suggest that chitosans exhibit harmful biological effects when administered parenterally. For example, chitosan has been shown in some studies to cause a haemostatic effect and activation of complement following administration to an animal. Moreover, some studies suggest that chitosan induces pro-inflammatory cytokines or chemokines after administration. For example, intraperitoneal (IP) administration of chitosan has been shown to induce a large number of macrophages with hyperplasia in the mesenterium of mice and causes severe peritoneal adhesions in rabbits. In order for nanoparticles to be compatible with parenteral applications, the nanoparticles should not activate immune cells in the bloodstream (monocytes, platelets, leukocytes, and dendritic cells) or in tissues (resident phagocytes) because such activation could cause premature removal of the nanoparticles from the body, and/or elicit inflammatory responses in the body, following administration.
Therefore, there exists a need for chitosan derivatives that can be safely and effectively used as nanoparticles for parenteral administration to animals. Moreover, new and effective methods of utilizing a chitosan derivative, or compositions containing a chitosan derivative, are also very desirable. Accordingly, the present disclosure provides chitosan derivatives and methods of using the chitosan derivatives that exhibit desirable properties and provide related advantages for improvement in safety and efficacy after administration.
Additionally, chitosan derivatives may be advantageously utilized to aid in the delivery of other pharmaceutical compositions, such as dendrimers. Polyamidoamine (“PAMAM”) dendrimers have previously been explored as pharmaceutical compositions for the delivery of therapeutic or imaging agents. PAMAM dendrimers can have various functional groups on their surface, for example amines, carboxylates, and amidoethylethanolamines. In particular, amine-terminated PAMAM dendrimers may be useful for gene delivery to animals because of their cationic charge, which allows for complexation of nucleic acids and for cellular uptake of the dendrimers. Moreover, protonation of tertiary amines in the interior of PAMAM dendrimers may facilitate endosomal escape via a “proton sponge” effect. Amine-termini of PAMAM dendrimers may also be useful for covalent conjugation of drugs via linkers cleaved by a condition unique to target tissues.
However, despite their ability to carry various agents, amine-terminated PAMAM dendrimers are generally not useful for systemic applications because of the non-specific toxicity and high risk associated with uptake by the reticuloendothelial system (RES). In an attempt to reduce the charge-related toxicity and prevent opsonization of cationic PAMAM dendrimers, a portion of their amine termini may be modified with polyethylene glycol (PEG), a hydrophilic linear polymer that masks the cationic charge. However, even after modification with polyethylene glycol (i.e., “pegylation”), modified PAMAM dendrimers can be disadvantageous due to the interference of PEG with the target cells. For example, PEG can interfere with important interactions between the carrier and the target cell, causing cellular uptake of the dendrimers to potentially be reduced. Even further modification of the pegylated PAMAM dendrimers with folate, transferrin, or RGD peptide (i.e., ligands known to enhance interactions with target cells) does not solve the problems because the fraction of target cells that express corresponding cellular receptors is not always predictable, and the expression level can change during progression of the disease(s) to be treated.
Therefore, there exists a need for the modification of dendrimers (e.g., PAMAM dendrimers) to provide for their safe and effective administration to animals. Moreover, new and effective methods of utilizing such modified dendrimers are also very desirable. Accordingly, the present disclosure also provides a nanoparticle structure comprising a derivative of chitosan and a dendrimer, as well as methods of using the nanoparticle structure, that exhibit desirable properties and provide related advantages for improvement in administering dendrimers to animals.